The present application relates to an electronic device, a method of producing the same, a light-emitting diode display unit, and a method of producing the same.
An example of various electronic devices produced by mounting fine elements on a substrate for a display unit is a light-emitting diode display unit. In such a light-emitting diode display unit, red-light-emitting diodes function as red-light-emitting subpixels, green-light-emitting diodes function as green-light-emitting subpixels, and blue-light-emitting diodes function as blue-light-emitting subpixels. The light-emitting diode display unit displays color images on the basis of the light-emitting state of these three types of subpixels.
A light-emitting diode display unit normally includes a plurality of first wirings extending in a first direction, a plurality of second wirings extending in a second direction different from the first direction, and a plurality of light-emitting diodes each having a first connecting portion and a second connecting portion. The light-emitting diodes are disposed on areas where the first wirings and the second wirings overlap. The first connecting portion (one electrode) of each of the light-emitting diodes is connected to a first wiring and the second connecting portion (another electrode) is connected to a second wiring.
In general, a large number of light-emitting diodes are formed in an array on a substrate (hereinafter also referred to as “substrate for element production”) such as a compound semiconductor substrate. Each of the light-emitting diodes is then moved (for example, transferred) from the substrate for element production to a substrate for a display unit. Each of the light-emitting diodes formed on the substrate for element production includes a first compound semiconductor layer of an n-conductivity type, an active layer, and a second compound semiconductor layer of a p-conductivity type that are sequentially formed. Furthermore, a p-side electrode is provided on the second compound semiconductor layer, and an n-side electrode is provided on the first compound semiconductor layer.
For example, a full high-definition (HD) high-fineness full-color display unit having a diagonal of 40 inches includes 1,920 pixels in the horizontal direction of the screen and 1,080 pixels in the vertical direction of the screen. Accordingly, in this case, the number of light-emitting diodes to be mounted is 1,920×1,080×(the number of types of light-emitting diodes, namely, a red-light-emitting diode, a green-light-emitting diode, and a blue-light-emitting diode, required for forming a single pixel), that is, about 6,000,000. Accordingly, a known step transfer method (step mounting method) is used as a method of mounting such a huge number of light-emitting diodes on a substrate for a display unit having a nominal diagonal of 40 inches. In this step transfer method, light-emitting diodes are formed in an array such that the array has a size smaller than the screen size, and the light-emitting diodes are sequentially transferred from being disposed on the light-emitting diode array to being mounted on a substrate for a display unit while the positions of the light-emitting diodes are adjusted.
Such a step transfer method is disclosed in, for example, Japanese Unexamined Patent Application Publication Nos. 2004-273596 and 2004-281630. In the techniques disclosed in these publications of unexamined patent applications, a substrate for a display unit having a pressure-sensitive adhesive layer thereon is used. Fundamentally, among a plurality of light-emitting diodes formed on a substrate for element production, predetermined light-emitting diodes are transferred to a transfer substrate in a state in which the light-emitting diodes are separated from the substrate for element production. Subsequently, the light-emitting diodes are transferred from being disposed on the transfer substrate to being embedded in a pressure-sensitive adhesive layer of a substrate for a display unit so that the light-emitting diodes partly protrude therefrom. The light-emitting diodes are then deeply embedded in the pressure-sensitive adhesive layer with a roller or the like. Thus, the light-emitting diodes are mounted on the substrate for a display unit (see, for example, paragraphs [0045] to [0048] of Japanese Unexamined Patent Application Publication No. 2004-273596 and paragraphs [0038] and [0046] of Japanese Unexamined Patent Application Publication No. 2004-281630).
In order to produce a light-emitting diode display unit, as described above, light-emitting diodes are mounted on a substrate for a display unit at predetermined intervals and pitches. A first insulating layer is then formed over the entire surface of the substrate. First openings are then formed in the first insulating layer at positions corresponding to the upper part of electrodes of the light-emitting diodes, and first wirings connected to the electrodes are formed on the first insulating layer. Subsequently, the first insulating layer including the first wirings is bonded to a holding substrate with an adhesive therebetween. Subsequently, the light-emitting diodes are separated from the substrate for a display unit by, for example, a laser ablation method, and a second insulating layer is formed over the entire surface. Second openings are then formed in the second insulating layer at positions corresponding to the upper part of other electrodes of the light-emitting diodes, and second wirings connected to the other electrodes are formed on the second insulating layer. The first wirings and the second wirings are connected to a driving circuit, thus producing a light-emitting diode display unit in the related art.